CEMB USA C218 User Manual - Manual (Page 15)

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Use and maintenance manual Rev. 04-2011
ENGLISH
5.5.1 Presetting of tolerance on the
machine
There is no general rule concerning acceptability of an eccen-
tricity value . As a fi rst approximation we consider it correct
to use a threshold of 1 to 1.5 mm. The E/ECE/324 standard
prescribes 1.5 mm as max. eccentricity of a rebuilt tyre.
5.5.2 Value of static unbalance, correlated
with eccentricity
Clear indication is given in the Measurement screen of both
the value and position of the static unbalance as well as the
eccentricity. In fact, it is interesting to check the correlations
of the two values, above all of the two positions. When the
two positions have a similar angle (± 30° one from the other),
there is a clear sign that an eccentricity is present which
can be compensated by matching.
5.5.3 Value of unbalance corresponding to
eccentricity
For user’s reference, the centrifugal force is calculated corre-
sponding to a certain speed, compared to the force generated
by the eccentricity present on the tyre (calculated with an
approximate average elastic constant).
5.6 ECCENTRICITY MEASUREMENT
(OPTIONAL)
The much enlarged fi gures show the outer tyre surface and
axis of wheel rotation.
GRAPH 1 (yellow) : represents the actual Peak-to-Peak
eccentri-city.
GRAPH 2 (red) : represents the eccentricity of the 1st harmo-
nic. For a wheel in optimum conditions, such graph should
approach a straight line.
While rotating the wheel, the screen cursor indicates the
current value, with the stage referred to the eccentricity me-
asurement sensor.
The following buttons are enabled:
Start an eccentricity optimisation procedure (see
ECCENTRICITY OPTIMISATION ).
A box is displayed indicating the offset effect that
that eccentricity of the fi rst harmonic measured
may have, at an average speed of 120 Km/h.
Return to measurement screen.
Use of the wheel balancer
Fig. A - shows measurement of the total Peak-to-Peak
eccentricity defi ned as maximum radial deviation of the tyre
surface.
Fig. B - shows measurement of the eccentricity of the 1st
harmonic, i.e. the eccentricity of that circle which “recopies”
the tyre shape, by averaging the local deviations of the tyre
from the round shape.
Obviously the P.P. measurement is normally greater than that
of the 1st harmonic. Tyre manufacturers normally supply two
different tolerances for the two eccentricities.
At the end of the balancing spin it is possible to automatically
measure the eccentricity of the tyre through the SONAR sensor
installed on the guard. The sensor should be positioned by
hand in front of the tyre tread.